How can a hurricane reverse the flow of massive rivers?

Question

Using Ida reversing the Mississippi as an example, sounds pretty insane to me.

In: Earth Science

Answer 1

The end of the Mississippi as it reaches the ocean has a very gradual slope. The river’s elevation only drops a few feet over the last several miles.

One of the hurricane’s effects is “storm surge”, it raises the ocean’s surface level at the shore by 10,15, 20 feet. This is caused by the wind physically pushing water onto the shore and by the low air pressure of the storm allowing the ocean to rise higher.

So now you’ve got the ocean 20 feet higher at the shore than it usually is. That puts the ocean’s water level higher than the river’s water level for miles back inland. So the ocean water freely flows back up the river channel until the river channel is as high as the storm-surge water level down at the coast.